Hemoglobin binding

I was given the oxygen binding curves for human and crocodile hemoglobins, with the crocodile having a higher affinity for oxygen at p50.
My questions are,
1) Crodocile hemoglobin does not bind BPG. Instead, deoxyhemoglobin preferentially binds to HCO3-. How does bicarbonate binding affect the p50 of crocodile hemoglobin binding to oxygen?
2) How does the crocodile deoxyhemoglobin's affinity for HCO3- help it feed?

Can someone please give me hints as to how to approach this problem? If you can explain the concepts to me that would be great!
Thank you so much!!